RAISE-TAQS: Nonlinear Optical Properties and Novel Quantum Phases of Polar Molecules in Optical Lattic

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Developing novel molecular materials relies on the ability to synthesize the constituents (molecules) and assemble them under carefully controlled conditions. The physical properties are determined by parameters like the molecular spacing, degree of order, and orientation. These parameters are typically fixed by self-assembly into the equilibrium crystal state and can only be changed by synthesizing a new batch of materials. This award supports research to use optical trapping methods to prepare molecular assemblies where these parameters can be tuned by external fields. This capability will permit the study of basic properties of solid-state materials in a cheaper, more flexible way. Polar molecules will be trapped in optical lattices, mimicking the molecular arrangement and properties of a solid crystal, and be oriented using external electric fields. Such a lattice configuration renders systematic tuning and exploration of relevant properties of solids feasible. Furthermore, this approach has the potential to explore novel quantum phenomena, like collective optical response, in such systems. In the future, this research has the potential to inform the synthesis of real molecular materials, from molecular crystals to nanocrystal assemblies to metal-organic frameworks. It provides a new approach to "crystal engineering" by combining advances in Physics, Chemistry and Materials Science. The project's broader impacts include student training in various areas, including lasers, vacuum technology and optical setups, as well as providing a broader, interdisciplinary research experience than typically accessible. Finally, regular visits to K-12 schools to present experimental demonstrations and lectures on trapping and manipulating particles, e.g. molecules or ions, will be part of this research effort.The main objective of this project is to load a quantum degenerate gas of polar AlCl molecules into an optical lattice to study novel quantum phases and simulate solid-state crystalline materials. This research has four specific goals: First, perform precision measurements of molecular properties, such as the energy spectrum and the Franck-Condon factors of AlCl; Second, cool the polar AlCl molecules to quantum degeneracy and study the dynamics and stability of dipolar Bose-Einstein condensates. The group will also explore correlated phases due to the anisotropic dipole-dipole interaction, including liquid crystal and density-wave phases, and probe the interplay between superfluidity and charge-ordering in low-dimensional materials; Third, create a one-dimensional optical lattice of polar molecules and study its non-linear optical response by measuring the second harmonic generation. By varying temperature and ordering, the optical lattice can be tuned from the limit of independent, noninteracting molecules to a strongly correlated one-dimensional crystal; Fourth, use Raman scattering to explore the transition from intramolecular vibrations of noninteracting molecules to intermolecular phonon structure by continuously tuning the lattice parameters. The experiments will demonstrate that ordered structures of diatomic molecules can exhibit phenomena that are directly relevant to solid-state materials. These results will motivate future experiments to expand the lattice to two dimensions and finally to fully mimic three-dimensional crystal systems. Their low temperature and tunable structure could lead to totally new phenomena, like giant nonlinear optical susceptibilities, that could inspire new research directions in the field of "crystal engineering".This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.